Molecular Genetics

Chargaff’s Rule – What is Chargaff’s Rule of Base Pairing?

What is Chargaff’s Rule?

Chargaff’s rule is something that relates to the DNA of a species. Also, it is named after its founder Erwin Chargaff. Furthermore, in this, we will discuss what is Chargaff’s rule. 

chargaff's rule

Erwin Chargaff

By profession, he was an Austro-Hungarian biochemist, who colonized in the U.S. during the Nazi era. Moreover, he was a professor of biochemistry at Columbia University Medical School.

 Besides, in his career, he discovered two major rules that helped the discovery of the double helix structure of the DNA.

According to his first rule, the DNA is the number of cytosine unit is equal to the guanine unit. In addition, the number of thymine unit is equal to the adenine units. Besides, it hinted that the base pair makeup of DNA.

The second rule states that the amount of cytosine, guanine, adenine, and thymine vary from species to species. Also, this hinted that DNA is not only a protein but could be genetic material.

Chargaff’s Rule

The accepted tetranucleotide hypothesis, most works assumed the derivations from the equimolar base ratios were because of experimental error. Also, Chargaff through experiment shows that the base composition of species varies among species.

However, in all the species the molar ratios [A] = [T] and [C] = [G], and that ratio [C + G] / [A + T] was typically less than the unity with [C + G] is less abundant. And these ratios are referred as Chargaff’s rule.

Moreover, the molar likenesses of A vs T and C vs G instinctively advocate specific sort of combination connection. Besides, Chargaff himself refuse to risk on the allegation of his experimental observation in the non-appearance of further experimental suggestion.

Furthermore, he regarded Watson and Crick’s model building as a scientifically unsound approach. Most noteworthy, he afterward defamed molecular biology in general, and finally, become disillusioned over what he regarded as a failure to admit the importance of his data.

Chargaff’s Rule of Base Pairing

In the Chargaff’s rules of base pairing are:

  • Relation of A with T: The Pyrimidine Thymine (T) always pairs with the Purine Adenine (A)
  • Relation of C with G: The Purine Guanine (G) always pair with the Pyrimidine Cytosine (C)

It is steady with there not being enough space (20 Å) for two purines to fit within the spiral and too much space for two pyrimidines to get near enough to each other to form hydrogen bonds among them.

But, the question is why A do not bond with C and G with T?

They only have the opportunity to establish hydrogen bonds between A and T and C and G. Moreover, they have the ability to form hydrogen bonds that makes the base pairs more stable structurally.

We call this base pair relation as Chargaff’s rules of DNA base pairing. Also, it tells us if we can read the sequence of nucleotides on one strand of DNA, and we can immediately deduce the complementary sequence on the other strand.

Furthermore, the rule of base pairing explains the phenomenon that whatever the amount of adenine (A) in the DNA of an organism, and the amount of thymine (T) is the same (Chargaff’s rule). In the same way, the amount of guanine (G) and the amount of cytosine (C) are also same.

Also, the C + G : A + T ratio various from organism to organism between the prokaryotes.

Solved Question for You

Question. In which year Erwin Chargaff died?

  1. 2012
  2. 2010
  3. 2002
  4. 2000

Answer. The correct answer is option C. Erwin Chargaff dies in the year 2002.

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